The invention relates to an apparatus for pressing a rack against a pinion of a steering gear assembly.
Rack-and-pinion steering systems for motor vehicles are well-established state of the art in various embodiments. Because of their functional principle, all rack-and-pinion steering systems include a steering gear assembly with a rack and a pinion wherein the pinion and a toothed portion of the rack form intermeshing gears. A rotational force applied via a steering wheel on a steering shaft and the pinion is transformed by the steering gear assembly into an axial force of the rack and remitted to steerable wheels of the motor vehicle. Nowadays, the rack-and-pinion steering systems are usually designed as hydraulic, electro-hydraulic or electric power-steering mechanisms supporting a driver during steering operation.
Since considerable forces occur in the steering gear assembly occasionally, it was realized soon that special provisions have to be made in order to keep the rack and the pinion in an engagement substantially free of play or backlash. Otherwise, there is a risk that the rack moves away from the pinion by a deformation transverse to its longitudinal direction when a load is applied. This would lead to an undesirable increasing backlash at least and, in an extreme case, even to a slip in the steering system.
In order to prevent such steering behavior, a support yoke is usually provided near the pinion, this support yoke providing a pressure force as constant as possible to urge the rack against the pinion. The greatest challenges for such yoke are that the designated pressure force is kept as constant as possible, a compensation of wear due to sliding friction between the support yoke and the rack during steering operation and an avoidance of disturbing rattle noise during motor vehicle operation.
In order to provide an improved steering gear assembly that inhibits the development of rattle even after the rack and the pinion have been subjected to wear, U.S. Pat. No. 7,930,951 B2 suggests a rack-and-pinion steering gear with a self-adjusting rack bearing. Therein, a compliance zone allowing the support yoke to move in response to dimensional variations in the pinion shaft and the rack during operation of the steering gear assembly should be kept as constant as possible by screwing a first adjustment member towards the support yoke depending on the wear occurring in the steering system. However, an exact axial adjustment by a rotational movement of the first adjustment member is hardly possible because of the considerable axial preload acting on the first adjustment member. To generate a screwing movement of the first adjustment member at all, an expensive torsional spring providing a high torsional moment is necessary. This leads to a rather complex assembly of the provided adjustable rack bearing.